Modeling and optimization of a membrane-assisted hybrid gas grid for methane and carbon dioxide transport, storage, and sector coupling

Decarbonizing the energy system requires large-scale integration of renewable energy, but its variability presents challenges for reliability and long-duration storage. Power-to-gas technologies present a promising solution by converting surplus electricity into gaseous fuels. Nonetheless, current approaches often overlook the carbon cycle in the system and the potential of natural gas infrastructure as a storage medium. This study proposes and evaluates an integrated renewable power-to-gas and hybrid gas grid system that retrofits pipelines to enable the co-injection of CH 4 and CO 2 , where a dynamic carbon cycle is established using membrane-based gas separation. The system is modeled through a mixed-integer linear programming (MILP) optimization framework combined with a quasi-dynamic gas grid model, capturing both operational and compositional effects. The model undergoes a year-long simulation based on varying electricity and gas demand profiles and market information. Results indicate that the hybrid gas grid is technically feasible and economically competitive, particularly for long-distance transmission and seasonal storage. An optimal CO 2 concentration of 30 % in the gas grid minimizes the levelized cost of methane (LCOM) to 0.378 EUR/kg. The findings provide valuable insights for retrofitting gas grids to support renewable integration, carbon cycle, and sector coupling under future low-carbon energy scenarios. • Retrofitting the gas grid for energy storage and the carbon cycle supports sector coupling. • Advanced membrane technologies facilitate a dynamic carbon balance. • The proposed system is both technically feasible and economically competitive. • The dynamic gas grid model is integrated into the techno-economic optimization framework. • A minimum energy storage price of 0.371 EUR/kg of methane is achieved.